Level ceiling

My husband and I are new homeowners in the process of having the entire first floor of our house renovated - a complete gut job down to the studs on all the walls and ceilings. The new sheetrock was just put up, taped, mudded and primed. The trouble is that the new ceiling is wavey in at least a half dozen different locations. The contractor said there's nothing he can do about it because our existing ceiling joists are uneven. Is it unreasonable to expect a level ceiling? Is shimming or other leveling techniques considered going above and beyond?